Various cushion materials made of polyester fiber have been developed. However, no product showing no strain by compression load and having voluminous feel has been prepared.
We have investigated and developed a method for the preparation of a cushion material, which can be used as a bed mat and the like and has a voluminous feel and a high quality, by using a conjugate fiber consisting of polyester (Japanese Laid-Open Patent Publication No. 152050 of 1990).
The method consists of a procedure in which polyester fibers (A) are mixed with core-sheath type composite or conjugate fibers (B) in which a sheath component of a lower melting point than that of the core component is used in a specified ratio and the resultant card web is temporarily melt-adhered with far-infrared ray or with a hot air circulating heater and the temporarily adhered webs are laminated according to the desired density and thickness and then the laminated webs are heated to melt-adhere each layer forming the laminate mutually. The method could prepare a cushion material of approximately 10 cm thick.
However, in the case that the webs are horizontally laminated and continuously heated in dry air, an increased thickness restricts the uniformity of the density and heat transmission. Also, in the case of a batch steaming system, an excessive thickness gives a vertical density gradient by the weight of the fibers themselves and results in an uneven product. Therefore, even the method described in Japanese Laid-Open Patent Publication No. 154050 of 1990 could not prepare stably a cushion material of as high a thickness as 20 cm or 50 cm in a uniform density.
Thus, the object of the present invention is to eliminate the disadvantages of the conventional technologies as mentioned above and to provide a product by using polyester fibers, which is an ultra-bulky block fiber aggregate having a high thickness of at least 20 cm, preferably 100 cm, and a uniform density in all of three directions like a urethane foam and can be used as a cushion material and a shoulder pad when sliced, and also to provide a method for the stable preparation thereof.